What Happens In Photosystem 1

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jerveelim | College Teacher | (Level 1) Honors

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Photosynthesis converts the light energy from the sun into chemical energy that is useful for the plants. There are two photosystems acting in series within the thylakoid membranes of the chloroplast that catalyze the light induced charge separation: Photosystem I (PSI) and Photosystem II(PSII). The numbers indicate the order in which the photosystems were discovered. Under normal conditions, electrons flow from PS II through cytochrome bf to PSI.

Photosystem I (PSI) optimally absorbs photons of  wavelength of 700 nm. It is responsible for providing high energy electrons with which to reduce NADP+ to produce NADPH to be used in the Calvin cycle.

Once the chlorophyll P700 gets excited, it will transfer the electron to a set of 4Fe-4S clusters.From these clusters the electron is
transferred to ferredoxin (Fd) a water soluble mobile electron carrier located in the stroma which contains a 2Fe-2S cluster coordinated to 4 cysteine residues.  The electron transfer produces a positive charge on the special pair which is neutralized by the transfer of
an electron from a reduced plastocyanin. The transfer of electrons is from reduced ferredoxin to NADP +(catalyzed by ferredoxin-NADP +  reductase which is flavoprotein). This complex contains a tightly
bound FAD which accepts the electrons one at a time from ferredoxin.  The FADH2 then transfers a hydride to NADP + to form NADPH.

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babai2 | Student, Undergraduate | eNotes Newbie

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In eucaryotic cells and cyanobacteria, there are two kinds of antennas associated with two different photosystems. Photosystem I absorbs longer wavelength light (680 nm) and funnels the energy to a special chlorophyll a molecule called P700.

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